When winding cheeses, a distinction is basically made between two types of windings: a. precision winding, and b. random winding. With precision winding, there is a constant relationship between the number of bobbin revolutions and the speed of the yarn cross winding during the entire bobbin travel, so that the winding ratio remains the same during the entire winding process. However, the yarn crossing angle decreases with increasing bobbin diameter. No pattern zones occur with a "precision winding" type of cheese winding operation. The bobbin has a high winding density and has satisfactory unwinding properties, because of which high draw-off speeds can be achieved. But the solidity of the yarn body is limited because of the constantly decreasing yarn crossing angle with the increase of the bobbin diameter. Moreover, the decreasing yarn crossing angle causes an increase of the winding density toward the edges, which can result in an uneven penetration of dyeing liquor in a dye process.
With random winding there is a fixed relationship between the velocity of the peripheral or circumferential surface of the bobbin and the speed of yarn cross winding. The yarn crossing angle is kept constant by this relationship, while the winding ratio, i.e. the number of bobbin turns per double lift, becomes smaller with increasing diameter. The advantages of random winding lie in that it is possible to create relatively solid yarn bodies with "random winding", which have a very even density.
However, it is disadvantageous that the decrease of the winding ratio is hyperbolic and that in certain ranges of the winding ratio wherein, for example, the winding ratio has a whole-number value, so-called patterns or reflex patterns are created. In these so-called pattern winding zones, the yarns of several successive winding layers lie on top of or very closely next to each other. The patterns result in the cheese being denser in these areas, so that, for example, uneven coloring can result during dyeing. There is the additional danger that the yarn areas which are placed on top of, or closely next to each other, laterally slide on top of each other and in the process become jammed, which has very disadvantageous results for the unwinding properties of a cheese.
Therefore numerous devices and methods have been developed in the past, which are intended to prevent the creation of the above mentioned pattern winding zones. For example, a pattern disruption method for preventing pattern windings is known from European Patent Document EP 0 399 243 B1 wherein, starting from a basic number of revolutions, a friction roller in the form a grooved roller is braked and then accelerated again in short intervals by means of the drive motor such that slippage occurs during acceleration as well as during braking.
A pattern disruption method is also known from German Patent Publication DE 42 39 579 A1, wherein the number of revolutions of a yarn guiding cylinder and the number of revolutions of a cheese are detected, and the measured results are evaluated in a computer in such a way that it can be determined at what time during the winding process a winding ratio range, which causes the generation of patterns, is passed. In this so-called pattern winding zone the cheese is braked by the bobbin brake in relation to the yarn guiding cylinder such that slippage is generated between them. Following passage through the pattern winding zone, the bobbin brake is released again, so that the cheese is once again driven without slippage. No defined reduction of the number of revolutions of the cheese is provided in the pattern winding zone with this method and is also not possible with the known device.
Moreover, pattern disruption methods have also been proposed in which the contact pressure of the cheese on the yarn guiding cylinder is varied. For example, a pattern disruption method is known from German Patent Publication DE 33 24 889 A1, wherein the cheese held in the creel is continuously lifted to different heights in such a way that the contact between the cheese and the yarn guiding cylinder continuously changes in respect to the length of time and the contact pressure. In addition, the drive of the yarn guiding cylinder is turned on and off in a constantly changing manner.
A winding device is known from German Patent Publication DE 39 27 142 A1, in which the contact pressure of the cheese on the yarn guiding cylinder can be reduced in a pattern winding zone. With this known winding device the creel is connected with an electro-mechanical torque actuator, preferably a d.c. motor which operates from a standing start, and which in turn is connected to a control device. The bobbin brake can furthermore be actuated via the control device. When a pattern winding zone is encountered, the creel is acted upon by the torque actuator in a "relief" direction, while the cheese held in the creel is simultaneously braked.
The pattern disruption methods of the prior art have so far not been satisfactory in actual use, since no exact regulation of the angular velocity of the cheese in the pattern winding zone had been provided by these methods. By means of the known devices it has been impossible to maintain a preset angular velocity with sufficient accuracy, either by regulating the contact pressure, with which the cheese rests on the yarn guiding cylinder, or via the bobbin brake.
Continuous problems have arisen with the known pattern disruption method because of the appearance of so-called remaining patterns, in particularly in the end phases of the cheeses in which few slippages occur.